But Northern Ireland’s First Minister and DUP leader Peter Robinson said the timing of the questioning in relation to the McConville case was down to Mr Adams himself. The Sinn Féin president chose the time and could have chosen any other date over the past seven weeks, he said.

Sinn Féin deputy leader Mary Lou McDonald said this morning in Dublin that Mr Adams was not a suspect in the PSNI investigation, repeating the party’s claim that the timing of his ongoing interview was “political” on the part of the PSNI.

She denied Sinn Féin was seeking to undermine the police but said the party was concerned the timing of the arrest, coming amid local and European election campaigns, was “politically contrived”.

She said some elements within the DUP and the Traditional Unionist Voice party have been “shouting very loudly and looking for an arrest of Gerry Adams… because they want to exact a level of political damage on Sinn Féin.”

Mr McGuinness said the PSNI contained a “dark side” which was “maliciously and vehemently hostile to the peace process”.

“I know that we’ve seen that dark side flex its muscles in the course of the last couple of days,” he said.

But Mr Robinson said the PSNI must not allow ongoing election campaigns to deflect their investigations into the abduction and murder of McConville.

“He [Mr Adams] chose the time, he chose it to be during the process of an election campaign, and the police must not allow the election campaign to in any way deflect them from their duty - their duty to the community as a whole but particularly to victims.”

In the Republic, Taoiseach Enda Kenny said his party had no connection with the arrest of Mr Adams.

“I want to make it perfectly clear: parties in the South, and I speak for our own, have had absolutely no connection with this at all,” he said today.

“I hope the president of Sinn Féin, deputy Adams, answers in the best way that he can, the fullest extent that he can, the questions being asked about a live murder investigation by the PSNI,” he added.

Minister for Education Ruairí Quinn dismissed as a “ludicrous assertion” the claim that the arrest was politically motivated. The PSNI “would not take this action lightly,” he said.

Fianna Fáil, meanwhile, called on Ms McDonald to withdraw her remarks. “By moving so quickly to criticise a police investigation and question the motives of the officers involved, it is deputy McDonald who has introduced politics into this inquiry,” the party’s justice spokesman Niall Collins said.